A. Field of the Invention
The present invention generally relates to the field of removing acid gases from a gas stream. More particularly, the present invention relates to removing H2S, NOx, SOx, and other pollutants from gas streams through the absorption of the acid gases from concentrated gas streams and then the separate generation of useful by-products comprising carbonate, bicarbonate, nitrate, and/or sulfate.
B. Description of Related Art
Most of the energy used in the world today is derived from the combustion of carbon and hydrogen containing fuels such as coal, oil, and natural gas. In addition to carbon and hydrogen, these fuels can contain oxygen, moisture, and contaminants such as H2S, other sulfur-containing compounds that form SOx during combustion, nitrogen-containing compounds that form NOx during combustion, carbon dioxide, mercury, and other trace elements. Awareness to the damaging effects of the acid gas contaminants released during combustion, or present in the uncombusted fuel, triggers the enforcement of ever more stringent limits on emissions from power plants, refineries, and other industrial processes. Thus, pressures by regulators and the marketplace are increasing to achieve near zero emission of acid gas contaminants and to reduce CO2 emission.
Amine processes already exist, which can non-selectively remove CO2 and H2S from streams of flue gas. Nearly all amine processes seek to regenerate the amine, essentially using them as a catalyst; one commonly used in scrubbing CO2 and H2S from natural gas is diethanolamine (DEA). One of the downsides of many amine processes is that they suffer problems with formation of contaminants in the form of Heat Stable Amine Salts (HSAS), which reduce the efficiency of scrubbing in the system via the formation of salts of chloride, sulfate, formate, acetate, oxalate, cyanide, thiocyanide, and thiosulfate. Other issues amine systems commonly run into include injection chemicals concentrating in the amine system, hydrocarbons condensing in the system, and (insoluble) particulates or suspended solids building up in the amine system. A wide range of amine-based systems exist under different brand names, but most suffer from the problems listed above to some degree.
Removal of acid gases such as H2S and CO2 are necessary to comply with government regulation, and doing so more efficiently and at a lower capital cost is desired.